New monoclinic polymorphic variety of diamond formed of graphene layers

Using the density functional theory method, geometrically optimized structure and some properties of a new carbon diamond-like phase are calculated in the local density approximation. The phase crystalline lattice is monoclinic (P21/m). This phase can be obtained by compressing the graphite in the direction of [001]. As a result of calculations, values of the following characteristics of the phase have been determined: the sublimation energy is 8,67 eV/atom; the volume modulus is equal to 458 GPa; the Vickers hardness is 90,9 GPa; the band gap is 4,5 eV. The calculation of graphite transformation into the monoclinic phase under compression has shown that the pressure of phase transition is 60 GPa. The new diamond-like phase can be identified by a calculated X-ray powder diffraction pattern.